Stand structure, biomass and carbon stock along disturbance gradients in differently managed tropical forests of Assam, northeast India

Forest ecosystems play an integral role in climate regulation through carbon sequestration and storage. Tropical forests in Assam (northeast India) have undergone major degradation which has threatened the standing biomass and carbon sequestration potential of these forests, apart from altering the dynamics of the ecosystem. In the present assessment, protected forests (PA), reserved forests (RF) and village forests (VF) were studied to understand how disturbances, or the lack of it, influence the plant species diversity, stand characteristics, biomass and carbon storage. In each forest a belt transect 250m in length and 20m in width was laid for enumeration of all woody individuals having a diameter at breast height (dbh) ≥5 cm. Disturbance index, community parameters and biomass and carbon stock were computed for each study site. Species richness, density, basal area, biomass and carbon varied between the forests and exhibited a negative correlation with the disturbance gradients under the different forest management regimes. The mean aboveground biomass (AGB) was 172.90±12.98 Mg ha⁻¹ in the PAs, 82.89±8.47 Mg ha⁻¹ in the RFs and 88.48±19.89 Mg ha⁻¹ in the VFs. The corresponding mean belowground biomass (BGB) was 84.77±14.23, 40.81±1.50 and 40.20±8.18 Mg ha⁻¹ in the PAs, RFs and VFs, respectively. The mean AGB C stock was 81.95±6.16, 39.29±4.01 and 41.94±9.42 Mg C ha⁻¹ in the PAs, RFs and VFs, respectively. The BGB C stock ranged between 15.18 and 46.93 Mg C ha⁻¹ among the study sites. The AGB accumulation was greater in the diameter class >56 cm in the PAs and RFs, whereas in VFs the intermediate diameter classes accounted to 44−58% of the total AGB. Species richness and stand characteristics were affected by human-induced disturbances in the study sites irrespective of the existing management regime, which in turn influenced the biomass and C stock. The study emphasizes the need of enhanced management practices in the disturbed tropical forests of Assam, which have a large potential in sequestering atmospheric CO₂ and contributing to national development policies in climate change mitigation.